Electronic devices such as semiconductor devices and integrated circuits may be mounted on a variety of substrates. These substrates include ceramic and glass substrates as well as printed circuit boards which, for example, may be made from polymeric materials. In any case, one or more electronic devices may be mounted on each substrate.
The substrate and electronic device may be hermetically sealed to protect the device and associated wiring from contamination by the environment. The hermeticity of the package also offers protection against entrapped processing residues. One type of hermetically sealed package is illustrated in Chu et al. U.S. Pat. No. 3,993,123, the disclosure of which is incorporated by reference herein.
The present invention, however, is most concerned with non-hermetic packages (although the invention has applicability to hermetic packages as well), whether they be sealed or not. In this case, the electronic component (substrate or electronic device) may be left uncovered so that it is relatively unprotected from the environment. Alternatively, the electronic component may be encapsulated or covered in some way to offer more protection.
The protection offered by the covering layer (which may also be passivating in nature), however, is not complete. Even the best encapsulation materials are permeable; consequently, they offer only limited protection from the intrusion of gaseous contaminants from the ambient environment and no protection at all from entrapped processing residues.
Recognizing the deficiencies of the encapsulation and covering materials, it has been proposed to add complexing agents to these materials to complex with, and thus eliminate the deleterious effects of, ionic contaminants.
It is known that ionic contaminants, such as sodium, potassium and chlorine, can react with unprotected metallurgies to cause corrosion, and in some cases electromigration, which eventually result in degradation of the electrical integrity of an electronic component. A portion of these ionic contaminants are inherent in the encapsulation and covering materials. Others of the ionic contaminants originate from the material deposited during the processing of the electronic component which is subsequently captured or trapped in pores and basins within the package.
In order to alleviate the problem of ionic contaminants in the encapsulation materials, Wong U.S. Pat. Nos. 4,271,425 and 4,396,796, the disclosures of which are incorporated by reference herein, suggests the incorporation of crown ethers or cryptate ethers in the encapsulation or covering material. Due to the fact that such complexing agents are tied up in the encapsulation or covering material, they are remote from the sites on the substrate and device where other ionic contaminants occur and thus are of limited effectiveness in preventing the corrosion reaction that takes place due to these ionic contaminants. Conventional cleaning of the package prior to encapsulation or covering is generally ineffective in the removal of such ionic contaminants.
Crown ethers and cryptate ethers are both known complexing agents as illustrated by the Wong references. Pacey et al. U.S. Pat. No. 4,711,853, illustrates that potassium may be selectively extracted in the presence of sodium from a solution containing crown ethers. In general, the ability of crown ethers to selectively extract alkali and alkaline earth metal ions has been recognized in the art as reported by Pedersen, C. J., J. American Chemical Society, 89, 7017 (1967). Similarly, the ability of cryptate ethers to complex with anions and cations has been reported by, for example, Truter et al., Endeavour, 30, 142 (1971). Cryptate ethers and crown ethers can be grouped under the generic classification of crown compounds. The seminal work on crown compounds and their complexing characteristics is "Crown Compounds, their characteristics and applications" by Michio Hiraoka, Elsevier Scientific Publishing Company, New York (1982). The disclosures of these references are incorporated by reference herein.
Notwithstanding the previously known complexing properties of crown compounds and their uses in encapsulating materials for electronic devices, there nevertheless remains a need to improve the inhibition of corrosion in electronic packages.
Accordingly, it is an object of the present invention to improve the inhibition of corrosion in electronic packages.
It is another object of the present invention to inhibit the corrosion in electronic packages in a simple yet effective manner.
These and other objects of the present invention will become more apparent after referring to the following description.